CLEAR_CONTEXT Procedure

Namespace in which the application context is to be cleared. Required.

For a session-local context, namespace must be specified. If namespace is defined as Session Local Context, then client_identifier is optional since it is only associated with a globally accessed context.

For a globally accessed context, namespace must be specified. NULL is a valid value for client_identifier because a session with no identifier set can see a context that looks like the (namespace, attribute, value, username, null) set using SET_CONTEXT.

client_identifier

Applies to a global context and is optional for other types of contexts; 64-byte maximum

attribute

Specific attribute in the namespace to be cleared. Optional. the default is NULL. If you specify attribute as NULL, then (namespace, attribute, value) for that namespace are cleared from the session. If attribute is not specified, then all context information that has the namespace and client_identifier arguments is cleared.

Usage Notes

This procedure must be invoked directly or indirectly by the trusted package.

Any changes in context value are reflected immediately and subsequent calls to access the value through SYS_CONTEXT return the most recent value.

CLEAR_IDENTIFIER Procedure

This procedure removes the set_client_id in the session.

Syntax

DBMS_SESSION.CLEAR_IDENTIFIER;

Usage Notes

This procedure is executable by public.

CLOSE_DATABASE_LINK Procedure

This procedure closes an open database link. It is equivalent to the following SQL statement:

ALTER SESSION CLOSE DATABASE LINK <name>

Syntax

DBMS_SESSION.CLOSE_DATABASE_LINK (
dblink VARCHAR2);

Parameters

Table 132-4 CLOSE_DATABASE_LINK Procedure Parameters

Parameter

Description

dblink

Name of the database link to close

FREE_UNUSED_USER_MEMORY Procedure

This procedure reclaims unused memory after performing operations requiring large amounts of memory (more than 100K).

Examples of operations that use large amounts of memory include:

Large sorting where entire sort_area_size is used and sort_area_size is hundreds of KB.

Compiling large PL/SQL packages, procedures, or functions.

Storing hundreds of KB of data within PL/SQL indexed tables.

You can monitor user memory by tracking the statistics "session UGA memory" and "session PGA memory" in the v$sesstat or v$statname fixed views. Monitoring these statistics also shows how much memory this procedure has freed.

Note:

This procedure should only be used in cases where memory is at a premium. It should be used infrequently and judiciously.

Syntax

DBMS_SESSION.FREE_UNUSED_USER_MEMORY;

Return Values

The behavior of this procedure depends upon the configuration of the server operating on behalf of the client:

Dedicated server: This returns unused PGA memory and session memory to the operating system. Session memory is allocated from the PGA in this configuration.

Shared server: This returns unused session memory to the shared_pool. Session memory is allocated from the shared_pool in this configuration.

Usage Notes

In order to free memory using this procedure, the memory must not be in use.

After an operation allocates memory, only the same type of operation can reuse the allocated memory. For example, after memory is allocated for sort, even if the sort is complete and the memory is no longer in use, only another sort can reuse the sort-allocated memory. For both sort and compilation, after the operation is complete, the memory is no longer in use, and the user can call this procedure to free the unused memory.

An indexed table implicitly allocates memory to store values assigned to the indexed table's elements. Thus, the more elements in an indexed table, the more memory the RDBMS allocates to the indexed table. As long as there are elements within the indexed table, the memory associated with an indexed table is in use.

The scope of indexed tables determines how long their memory is in use. Indexed tables declared globally are indexed tables declared in packages or package bodies. They allocate memory from session memory. For an indexed table declared globally, the memory remains in use for the lifetime of a user's login (lifetime of a user's session), and is freed after the user disconnects from ORACLE.

Indexed tables declared locally are indexed tables declared within functions, procedures, or anonymous blocks. These indexed tables allocate memory from PGA memory. For an indexed table declared locally, the memory remains in use for as long as the user is still running the procedure, function, or anonymous block in which the indexed table is declared.After the procedure, function, or anonymous block is finished running, the memory is then available for other locally declared indexed tables to use (in other words, the memory is no longer in use).

Assigning an uninitialized, "empty" indexed table to an existing index table is a method to explicitly re-initialize the indexed table and the memory associated with the indexed table. After this operation, the memory associated with the indexed table is no longer in use, making it available to be freed by calling this procedure. This method is particularly useful on indexed tables declared globally which can grow during the lifetime of a user's session, as long as the user no longer needs the contents of the indexed table.

The memory rules associated with an indexed table's scope still apply; this method and this procedure, however, allow users to intervene and to explicitly free the memory associated with an indexed table.

Examples

The following PL/SQL illustrates the method and the use of procedure FREE_UNUSED_USER_MEMORY.

GET_PACKAGE_MEMORY_UTILIZATION Procedure

This procedure describes static package memory usage.

The output collections describe memory usage in each instantiated package. Each package is described by its owner name, package name, used memory amount, and unused allocated memory amount. The amount of unused memory is greater than zero because of memory fragmentation and also because once used free memory chunks initially go to a free list owned by the package memory heap. They are released back to the parent heap only when the FREE_UNUSED_USER_MEMORY Procedure is invoked.

Buffer to store a list of application context set in the current session

Return Values

Table 132-11 LIST_CONTEXT Procedure Return Values

Return

Description

list

A list of (namespace, attribute, values) set in current session

size

Returns the number of entries in the buffer returned

Usage Notes

The context information in the list appears as a series of <namespace> <attribute> <value>. Because list is a table type variable, its size is dynamically adjusted to the size of returned list.

MODIFY_PACKAGE_STATE Procedure

This procedure is used to perform various actions (as specified by the action_flags parameter) on the session state of all PL/SQL program units active in the session. This takes effect after the PL/SQL call that made the current invocation finishes running. The procedure uses the DBMS_SESSION constants listed in Table 132-13.

Syntax

DBMS_SESSION.MODIFY_PACKAGE_STATE(
action_flags IN PLS_INTEGER);

Parameters

Table 132-12 MODIFY_PACKAGE_STATE Procedure Parameters

Parameter

Description

action_flags

Bit flags that determine the action taken on PL/SQL program units:

DBMS_SESSION.FREE_ALL_RESOURCES (or 1)—frees all memory associated with each of the previously run PL/SQL programs from the session. Clears the current values of any package globals and closes cached cursors. On subsequent use, the PL/SQL program units are reinstantiated and package globals are reinitialized. Invoking MODIFY_PACKAGE_STATE with the DBMS_SESSION.FREE_ALL_RESOURCES parameter provides functionality identical to the DBMS_SESSION.RESET_PACKAGE() interface.

DBMS_SESSION.REINITIALIZE (or 2)—reinitializes packages without actually being freed and recreated from scratch. Instead the package memory is reused. In terms of program semantics, the DBMS_SESSION.REINITIALIZE flag is similar to the DBMS_SESSION.FREE_ALL_RESOURCES flag in that both have the effect of reinitializing all packages.

However, DBMS_SESSION.REINITIALIZE should exhibit better performance than the DBMS_SESSION.FREE_ALL_RESOURCES option because:

Packages are reinitialized without actually being freed and recreated from scratch. Instead the package memory gets reused.

Any open cursors are closed, semantically speaking. However, the cursor resource is not actually freed. It is simply returned to the PL/SQL cursor cache. The cursor cache is not flushed. Hence, cursors corresponding to frequently accessed static SQL in PL/SQL remains cached in the PL/SQL cursor cache and the application does not incur the overhead of opening, parsing, and closing a new cursor for those statements on subsequent use.

The session memory for PL/SQL modules without global state (such as types, stored-procedures) are not freed and recreated.

Usage Notes

See the parameter descriptions in Table 132-14 for the differences between the flags and why DBMS_SESSION.REINITIALIZE exhibits better performance than DBMS_SESSION.FREE_ALL_RESOURCES.

Table 132-13 Action_flags Constants for MODIFY_PACKAGE_STATE

Constant

Description

FREE_ALL_RESOURCES

PLS_INTEGER:= 1

REINITIALIZE

PLS_INTEGER:= 2

Reinitialization refers to the process of resetting all package variables to their initial values and running the initialization block (if any) in the package bodies. Consider the package:

Invoking function P2.foo and setting P.m to the value returned from P2.foo

Setting P.d to the return value of SYSDATE built-in

Closing cursor P.c if it was previously opened

Setting P.v to 'hello'

Running the initialization block in the package body

The reinitialization for a package is done only if the package is actually referenced subsequently. Furthermore, the packages are reinitialized in the order in which they are referenced subsequently.

When using FREE_ALL_RESOURCES or REINITIALIZE, make sure that resetting package variable values does not affect the application.

Because DBMS_SESSION.REINITIALIZE does not actually cause all the package state to be freed, in some situations, the application could use significantly more session memory than if the FREE_ALL_RESOURCES flag or the RESET_PACKAGE procedure had been used. For instance, after performing DBMS_SESSION.MODIFY_PACKAGE_STATE(DBMS_SESSION.REINITIALIZE), if the application does not refer to many of the packages that were previously referenced, then the session memory for those packages remains until the end of the session (or until DBMS_SESSION.RESET_PACKAGE is called).

Because the client-side PL/SQL code cannot reference remote package variables or constants, you must explicitly use the values of the constants. For example, DBMS_SESSION.MODIFY_PACKAGE_STATE(DBMS_SESSION.REINITIALIZE)does not compile on the client because it uses the constant DBMS_SESSION.REINITIALIZE.

Instead, use DBMS_SESSION.MODIFY_PACKAGE_STATE(2) on the client, because the argument is explicitly provided.

Examples

This example illustrates the use of DBMS_SESSION.MODIFY_PACKAGE_STATE. Consider a package P with some global state (a cursor c and a number cnt). When the package is first initialized, the package variable cnt is 0 and the cursor c is CLOSED. Then, in the session, change the value of cnt to 111 and also execute an OPEN operation on the cursor. If you call print_status to display the state of the package, you see that cnt is 111 and that the cursor is OPEN. Next, call DBMS_SESSION.MODIFY_PACKAGE_STATE. If you print the status of the package P again using print_status, you see that cnt is 0 again and the cursor is CLOSED. If the call to DBMS_SESSION.MODIFY_PACKAGE_STATE had not been made, then the second print_status would have printed 111 and OPEN.

Frequency at which we dump row source statistics. Value should be 'NEVER', 'FIRST_EXECUTION' (equivalent to NULL) or 'ALL_EXECUTIONS'.

RESET_PACKAGE Procedure

This procedure de-instantiates all packages in this session. It frees the package state.

Note:

See "SESSION _TRACE_ENABLE Procedure" . The MODIFY_PACKAGE_STATE interface, introduced in Oracle9i, provides an equivalent of the RESET_PACKAGE capability. It is an efficient, lighter-weight variant for reinitializing the state of all PL/SQL packages in the session.

Memory used for caching the execution state is associated with all PL/SQL functions, procedures, and packages that were run in a session.

For packages, this collection of memory holds the current values of package variables and controls the cache of cursors opened by the respective PL/SQL programs. A call to RESET_PACKAGE frees the memory associated with each of the previously run PL/SQL programs from the session, and, consequently, clears the current values of any package globals and closes any cached cursors.

RESET_PACKAGE can also be used to reliably restart a failed program in a session. If a program containing package variables fails, then it is hard to determine which variables need to be reinitialized. RESET_PACKAGE guarantees that all package variables are reset to their initial values.

Syntax

DBMS_SESSION.RESET_PACKAGE;

Usage Notes

Because the amount of memory consumed by all executed PL/SQL can become large, you might use RESET_PACKAGE to trim down the session memory footprint at certain points in your database application. However, make sure that resetting package variable values does not affect the application. Also, remember that later execution of programs that have lost their cached memory and cursors will perform slower, because they need to re-create the freed memory and cursors.

RESET_PACKAGE does not free the memory, cursors, and package variables immediately when called.

Note:

RESET_PACKAGE only frees the memory, cursors, and package variables after the PL/SQL call that made the invocation finishes running.

This SQL*Plus script runs a large program with many PL/SQL program units that may or may not use global variables, but it doesn't need them beyond this execution:

EXCECUTE large_plsql_program1;

To free up PL/SQL cached session memory:

EXECUTE DBMS_SESSION.RESET_PACKAGE;

To run another large program:

EXECUTE large_plsql_program2;

SET_CONTEXT Procedure

This procedure sets the context, of which there are four types: session local, globally initialized, externally initialized, and globally accessed.

Of its five parameters, only the first three are required; the final two parameters are optional, used only in globally accessed contexts. Further parameter information appears in the parameter table and the usage notes.

The client_id parameter must be a string of at most 64 bytes. It is case-sensitive and must match the argument provided for set_identifier.

If the namespace parameter is a global context namespace, then the username parameter is matched against the current database user name in the session, and the client_id parameter is matched against the current client_id in the session. If these parameters are not set, NULL is assumed, enabling any user to see the context values.

This procedure must be invoked directly or indirectly by the trusted package.

The caller of SET_CONTEXT must be in the calling stack of a procedure that has been associated to the context namespace through a CREATECONTEXT statement. The checking of the calling stack does not cross a DBMS boundary.

No limit applies to the number of attributes that can be set in a namespace. An attribute retains its value during the user's session unless it is reset by the user.

If the value of the parameter in the namespace has been set, SET_CONTEXT overwrites this value.

Any changes in context value are reflected immediately and subsequent calls to access the value through SYS_CONTEXT return the most recent value.

SET_EDITION_DEFERRED Procedure

This procedure requests a switch to the specified edition. The switch takes effect at the end of the current client call.

Syntax

DBMS_SESSION.SET_EDITION_DEFERRED (
edition IN VARCHAR2);

Parameters

Table 132-16 SET_EDITION_DEFERRED Procedure Parameters

Parameter

Description

edition

Name of the edition to which to switch. The contents of the string are processed as a SQL identifier; double-quotes must surround the remainder of the string if special characters or lower case characters are present in the edition's actual name and, if double-quotes are not used, the contents are set in uppercase. The caller must have USE privilege on the named edition.

SET_IDENTIFIER Procedure

This procedure sets the client ID in the session.

Syntax

DBMS_SESSION.SET_IDENTIFIER (
client_id VARCHAR2);

Parameters

Table 132-17 SET_IDENTIFIER Procedure Parameters

Parameter

Description

client_id

Case-sensitive application-specific identifier of the current database session

Usage Notes

SET_IDENTIFIER sets the session's client id to the given value. This value can be used to identify sessions in v$session by means of v$session.client_identifier. It can also be used to identify sessions by means of sys_context('USERENV','CLIENT_IDENTIFIER').

This procedure is executable by PUBLIC.

SET_NLS Procedure

This procedure sets up your Globalization Support (NLS). It is equivalent to the following SQL statement:

ALTER SESSION SET <nls_parameter> = <value>

Syntax

DBMS_SESSION.SET_NLS (
param VARCHAR2,
value VARCHAR2);

Parameters

Table 132-18 SET_NLS Procedure Parameters

Parameter

Description

param

Globalization Support parameter. The parameter name must begin with 'NLS'.

value

Parameter value.

If the parameter is a text literal, then it needs embedded single-quotes. For example, "set_nls ('nls_date_format','''DD-MON-YY''')".

SET_ROLE Procedure

This procedure enables and disables roles. It is equivalent to the SETROLE SQL statement.

Syntax

DBMS_SESSION.SET_ROLE (
role_cmd VARCHAR2);

Parameters

Table 132-19 SET_ROLE Procedure Parameters

Parameter

Description

role_cmd

Text is appended to "set role" and then run as SQL

Usage Notes

Note that the procedure creates a new transaction if it is not invoked from within an existing transaction.

SET_SQL_TRACE Procedure

This procedure turns tracing on or off. It is equivalent to the following SQL statement:

ALTER SESSION SET SQL_TRACE ...

Syntax

DBMS_SESSION.SET_SQL_TRACE (
sql_trace boolean);

Parameters

Table 132-20 SET_SQL_TRACE Procedure Parameters

Parameter

Description

sql_trace

TRUE turns tracing on, FALSE turns tracing off

SWITCH_CURRENT_CONSUMER_GROUP Procedure

This procedure changes the current resource consumer group of a user's current session.

This lets you switch to a consumer group if you have the switch privilege for that particular group. If the caller is another procedure, then this enables the user to switch to a consumer group for which the owner of that procedure has switch privilege.

If TRUE, then sets the current consumer group of the caller to his/her initial consumer group in the event of an error

Return Values

This procedure outputs the old consumer group of the user in the parameter old_consumer_group.

Note:

You can switch back to the old consumer group later using the value returned in old_consumer_group.

Exceptions

Table 132-22 SWITCH_CURRENT_CONSUMER_GROUP Procedure Exceptions

Exception

Description

29368

Non-existent consumer group

1031

Insufficient privileges

29396

Cannot switch to OTHER_GROUPS consumer group

Usage Notes

The owner of a procedure must have privileges on the group from which a user was switched (old_consumer_group) in order to switch them back. There is one exception: The procedure can always switch the user back to his/her initial consumer group (skipping the privilege check).

By setting initial_group_on_error to TRUE, SWITCH_CURRENT_CONSUMER_GROUP puts the current session into the default group, if it can't put it into the group designated by new_consumer_group. The error associated with the attempt to move a session into new_consumer_group is raised, even though the current consumer group has been changed to the initial consumer group.

Examples

CREATE OR REPLACE PROCEDURE high_priority_task is
old_group varchar2(30);
prev_group varchar2(30);
curr_user varchar2(30);
BEGIN
-- switch invoker to privileged consumer group. If we fail to do so, an
-- error is thrown, but the consumer group does not change
-- because 'initial_group_on_error' is set to FALSE
dbms_session.switch_current_consumer_group('tkrogrp1', old_group, FALSE);
-- set up exception handler (in the event of an error, we do not want to
-- return to caller while leaving the session still in the privileged
-- group)
BEGIN
-- perform some operations while under privileged group
EXCEPTION
WHEN OTHERS THEN
-- It is possible that the procedure owner does not have privileges
-- on old_group. 'initial_group_on_error' is set to TRUE to make sure
-- that the user is moved out of the privileged group in such a
-- situation
dbms_session.switch_current_consumer_group(old_group,prev_group,TRUE);
RAISE;
END;
-- we've succeeded. Now switch to old_group, or if cannot do so, switch
-- to caller's initial consumer group
dbms_session.switch_current_consumer_group(old_group,prev_group,TRUE);
END high_priority_task;
/

UNIQUE_SESSION_ID Function

This function returns an identifier that is unique for all sessions currently connected to this database. Multiple calls to this function during the same session always return the same result.

Syntax

DBMS_SESSION.UNIQUE_SESSION_ID
RETURN VARCHAR2;

Pragmas

pragma restrict_references(unique_session_id,WNDS,RNDS,WNPS);

Return Values

Table 132-23 UNIQUE_SESSION_ID Function Return Values

Return

Description

unique_session_id

Returns up to 24 bytes

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